There is acoustic cavity resonance produced by vibration of air with which the cavity of a tire is charged, which is one of the sources that create tire noise. The tread of a tire, which comes into contact with a road surface during running of a vehicle, vibrates due to unevenness of the road surface, and this vibration then causes the vibration of air in the cavity of the tire, thereby producing the cavity resonance. It is known that the frequency of sound caught as noise in the cavity resonance is generally about 200 Hz to 300 Hz, differing according to tire sizes. It is thus important to decrease the level of noise in this frequency band in order to reduce tire noise.
As an approach for reducing noise created by such acoustic cavity resonance, it has been proposed to add a sound absorbing member in the cavity of a tire to absorb the resonance sound (see Unexamined Japanese Patent Application Publication No. 62-216803, for example). However, since a sufficient study on the characteristics of the sound absorbing member is not made, it is not necessarily said that effective noise reduction has been achieved.